It is common and usual practice in sealing the top portion of rotary valves, as for example rotary plug valves, to use a top seal that seals against media leakage while simultaneously accommodating rotational movement of the valving element relative to a valve body. A rotary plug valve, for example, has a plug portion which is rotatably fitted within a valve body. This plug portion of the valve is joined by a stem or shaft portion which extends out of the valve body to interact with an actuator and transmit torque to the plug portion. This torque is used to rotate the plug portion within the valve body and to move a passageway in the plug portion of the valve in and out of registry with a flow passage extending through the valve body. In plug valves, it is common practice to seal the top of the valve with a centrally apertured diaphragm with the shaft portion of the valve extending through the central aperture of the top seal. In one type of conventional top seal, a delta ring bearing is circumscribed about the stem or shaft in an interference fit over the diaphragm. A thrust collar is then fitted over the delta ring to urge the delta ring both radially inward toward the rotary shaft and downwardly toward the rotary passageway of the valve. An example of this type of sealing arrangement is seen in U. S. Pat. No. 3,235,272.
Another successful top seal uses a diaphragm with a reversed lip which engages and extends along the stem's periphery. In this sealing arrangement, the diaphragm has a central opening through which the stem extends. The radially intermost portion of the diaphragm in engagement with the stem is folded so as to orient the internal periphery of the opening to extend axially along the stem. In this arrangement, the opening of the diaphragm for the stem is in substantially perpendicular relationship with the outermost and intermediate portions of the diaphragm.
An improvement over the second mentioned type of seal has a diaphragm which greatly resembles that of the reverse lip type seal mentioned above with the improvement including a conforming sealing member which is fitted within the groove formed by the fold of the diaphragm and which urges the intermost portion of the folded diaphragm portion into engagement with the stem.
While all of the above mentioned sealing arrangements have been highly satisfactory, they are not without their attendant disadvantages. For example, these seals are relatively expensive to manufacture and frequently require special assembly tools. Further, the nature of several of the above mentioned sealing designs require that the diaphragms be constructed through a forming operation and these manufacturing techniques impose limitations on the possible materials for the seals.
It is thus an object of the present invention to provide a one piece top seal that may be manufactured more economically than prior art seals of equivalent sealing capability.
It is a further object of the present invention to provide a top valve seal which provides for ease of replacement when the valve is serviced in the field and which does not require special assembly tools.
It is yet another object of the present invention to provide a top seal that may be formed by a machine operation and which may be formed of a large number of different materials.
It is yet another object of the present invention to provide a top seal design that may be used in a fire safe application.
It is yet another object of the present invention to provide a top seal in which the diaphragm thickness is not determined by the space between the valve plug and the thrust collar.